Prions are novel pathogens that are composed entirely of PrP^Sc, the self-templating conformation of the host prion protein, PrP^C. Prion strains are operationally defined as a heritable phenotype of disease that are encoded by strain-specific conformations of PrP^Sc. The factors that influence the relative distribution of strains in a population are only beginning to be understood. For prions with an infectious etiology, environmental factors, such as strain-specific binding to surfaces and resistance to weathering, can influence which strains are available for transmission to a naïve host. Strain-specific differences in efficiency of infection by natural routes of infection can also select for prion strains. The host amino acid sequence of PrP^C has the greatest effect on dictating the repertoire of prion strains. The relative abundance of PrP^C, post-translational modifications of PrP^C and cellular co-factors involved in prion conversion can also provide conditions that favor the prevalence of a subset of prion strains. Additionally, prion strains can interfere with each other, influencing the emergence of a dominant strain. Overall, both environmental and host factors may influence the repertoire and distribution of strains within a population.

朊病毒是完全由 PrP ^Sc组成的新型病原体，PrP Sc是宿主朊病毒蛋白 PrP ^C的自模板构象。^{朊病毒菌株在操作上被定义为一种可遗传的疾病表型，由 PrP Sc}的菌株特异性构象编码。影响种群中菌株相对分布的因素才刚刚开始被了解。对于具有传染性病因学的朊病毒，环境因素（例如与表面的菌株特异性结合和耐候性）会影响哪些菌株可用于传播给幼稚宿主。自然感染途径感染效率的菌株特异性差异也可以选择朊病毒菌株。^{PrP C}的宿主氨基酸序列对支配朊病毒菌株的所有组成部分具有最大的影响。^{PrP C}的相对丰度、PrP ^C的翻译后修饰和参与朊病毒转化的细胞辅助因子也可以提供有利于朊病毒菌株亚群流行的条件。此外，朊病毒菌株会相互干扰，从而影响优势菌株的出现。总的来说，环境和宿主因素都可能影响种群中菌株的库和分布。